This invention relates to a process for forming a metal or metal compound coating on a face of a freshly formed ribbon of hot glass during its travel from a flat glass forming installation, by contacting such face at a coating station with a fluid medium or fluid media comprising a substance or substances from which said coating metal or metal compound is formed on said face.
Processes of the foregoing kind are used for example for forming surface coatings which modify the apparent colour of the glass and/or which confer some other required property in respect of incident radiation, e.g. an infra-red-reflecting property.
In some such processes, the substance(s) from which the required coating is formed is or are supplied in the liquid phase, e.g. by spraying. In other cases the said substance(s) is or are supplied in the vapour phase.
Processes as referred to are particularly useful for forming good quality metal oxide coatings on ribbons of glass during their conveyance from the flat glass forming installation, e.g. a drawing machine or a float tank. The metal oxide coating can be formed by spraying the glass ribbon with a solution of a metal compound from which the metal oxide is formed in situ by chemical reaction or decomposition, e.g. by pyrolysis, on contact with the hot ribbon. A specific example is the formation of a tin oxide coating by spraying a solution of a tin chloride, with or without other ingredients. Alternatively a said metal oxide coating can be formed by contacting the hot ribbon with a stream of a vaporised metal compound e.g. a vaporised tin compound, and a stream of oxygen or oxygen-containing gas to cause an oxidation reaction with formation of the required metal oxide coating on the ribbon. Processes as referred to can however also be used for forming coatings of other metal compounds, e.g. for forming a coating of a metallic boride, sulphide, nitride, carbide or arsenide by reacting a corresponding metallic or organometallic compound with a halogenated boron compound, H.sub.2 S, NH.sub.3, CH.sub.4, or an arsenic containing compound, in the absence of oxygen. Metal coatings can be formed by contacting the glass ribbon in a reducing atmosphere or at least in the absence of oxygen, with a metal carbonyl, e.g. nickel carbonyl, which decomposes under the action of heat provided by the hot ribbon.
It is not easy to form coatings satisfying the high quality standards which the market sometimes demands. One important problem which is encountered is that of controlling the thickness of the coating so that it complies with given standards. The thickness of the coating forming on any region within the area of the glass ribbon is susceptible of the influence of various factors. These include not only the rate at which the fluid coating medium or media is or are supplied to the coating station but also the temperature conditions at that station. The temperature conditions of the glass at the coating station are of course determined primarily by the temperature to which the glass is heated in the flat glass forming installation, which in turn depends on the nature of that installation and the required specifications of the ribbon.
The temperature of the glass at the coating station is liable to vary in course of time and from one part of the ribbon to another. Such temperature differences may occur for example because of a change being effected in the thickness and/or speed of the glass ribbon, or because of the influence of convection currents circulating above and around the glass ribbon. Differences in glass ribbon temperature in course of time or across the ribbon can to some extent be compensated for by modifying the temperature at which the fluid coating medium or media is or are fed to the coating station, but it is not always convenient and in some cases it is not possible for the coating thickness to be influenced quickly enough or to the required extent in that way.